It is often desirable for small businesses (and others) who require only occasional use of a facsimile machine, to incorporate the machine with their already existing telephone line network without supplying it with a single dedicated line. In doing so, the business saves the cost of installation and service charges associated with a dedicated facsimile line.
A problem with such a shared line arrangement is that an incoming call cannot be identified as either a facsimile call or a voice call until it is answered by the facsimile machine or a person answers the connected telephone. The telephone "rings" the same in either case.
This inability to properly distinguish an incoming call prior to answering can lead to misplaced or unanswered incoming calls. For example, if a facsimile machine answers a voice call, the caller will become confused and possibly upset by the high pitch "handshake" signal transmitted from the facsimile machine. Likewise, if a person answers a facsimile call, the remote facsimile station will most likely abort transmission because it did not receive any return "handshake" signals. In either case, potentially important data transmission can be either lost or delayed, thus disrupting business transactions.
Facsimile machines are currently available with internal delaying circuitry which controls a delay period from the moment an incoming call is detected to when a facsimile machine answers the call. For example, the facsimile machine could answer an incoming call after a predetermined number of telephone rings, usually within the first ring. Upon answering any incoming call, voice or fax, a facsimile machine will immediately and continuously transmit return handshake signals along the single telephone line. If the incoming call happens to be a facsimile call from a remote facsimile station, the incoming handshake signals would be received by the local facsimile machine and the two machines would connect and begin data transmission. If however, the incoming call is a voice call, the facsimile machine would answer the call and begin transmitting return handshake signals for about 20 seconds. After not receiving the appropriate incoming handshake signals from the incoming voice call during this period, the facsimile machine would either disconnect the line or summon a person in the immediate area through the use of beeper, indicating a voice call. This situation causes inconvenience to the caller (incoming call) because he must listen to the outgoing handshake signals transmitted by the called facsimile station for about 20 seconds before any human is summoned to the telephone. He will most likely hang up.
Furthermore, after a facsimile machine answers a voice call, it could trigger an alarm which indicates a malfunction and, depending on the machine, could require resetting. If the facsimile machine requires resetting and no one is available to reset the machine, no future incoming facsimile calls will be received.
If an operator answers the facsimile machine and the incoming call is a voice call, the two parties will connect and communication can precede with no lost information. However, if an incoming call is a facsimile call and a human operator answers before the local facsimile machine, the remote facsimile station (calling) will not receive the important return handshake signals and will automatically disconnect after a short period of time. The remote station will have to try again to connect with the local facsimile machine.
In lieu of any practical solution, all known currently available facsimile machines which have this answering delay feature have answering priority over the telephone for all incoming calls. Apparently it is considered more important to successfully connect two facsimile machines and receive data, than possibly irritate a caller (voice) with handshake signals.
A similar inconvenience to a voice caller occurs when a voice call answering machine is connected to the fax/telephone shared line arrangement. After the above-mentioned 20 second period, the facsimile machine will summon a person from the immediate area or activate a connected voice answering machine.
Many aftermarket electronic devices have been made available in an effort to solve the abovementioned problems associated with sharing one telephone line with a facsimile machine and a telephone. These devices are connected to a portion of the telephone network and are generally concerned with answering an incoming call and thereafter determining the type of call, voice or fax. Some of these devices permit a human operator to interfere with the "handshake" procedure between two facsimile machines by answering an incoming facsimile call prior to a facsimile machine. With such devices, after hearing the incoming "handshake" signals from the remote facsimile station, the operator must push a "transfer button" on the device and hang up the phone before the incoming "handshake" signals automatically cease. If the operator fails to do this before the relatively short time period, the two facsimile machines will not connect and the incoming data will be lost.